1. Technical Field
The present invention relates generally to a contact lens and a method for manufacturing thereof. In particular, the invention relates to a contact lens having excellent oxygen permeability and a high refractive index and a method for manufacturing thereof.
2. Background Art
Recently, a growing number of people wear a contact lens, especially a soft contact lens. Since a contact lens is used directly in contact with the ocular mucous membrane, it needs to be maintained as clean as possible. Thus, it is also important to reduce the attachment of foreign matters such as bacteria and the like to the lens during wearing it. Although many of the conjunctiva bacteria are not pathogenic, once an excessive number of bacteria are attached to a contact lens, a biofilm is formed on the surface of the contact lens due to the extrabacterial materials, etc. secreted from the attached bacterial. The biofilm is in danger of being a breeding ground for pathogenic microorganisms which may increase the risk for bacterial infectious diseases.
Conventionally, an antibiotic-supported contact lens has been reported as a technique for controlling the attachment of bacteria to the contact lens (See, Prior Art Documents 1 and 2). However, such a contact lens is made antibacterial only by using a formulation for a contact lens ocular composition such as an eye drop, an eye wash, a contact lens care agent, etc. A technique for controlling the attachment of bacteria to the surface of a contact lens itself has not yet been researched adequately.    Prior Art Document 1: Japanese Laid-open Patent Publication No. 2003-248200    Prior Art Document 1: Japanese Laid-open Patent Publication No. 2009-533081
A practically developed contact lens is classified into a hard-type contact lens based on a polymethyl methacrylate and a soft-type contact lens based on a poly-2-hydroxyethyl methacrylate. However, because these contact lenses have poor oxygen permeability, they cannot be continuously worn for a long period of time due to the insufficient oxygen supply to the corneal tissue on the surface of the eyeballs. In order to improve the oxygen permeability, the use of a contact lens base material copolymerized or blended with silicone (See, Prior Art Documents 3 and 4) has been proposed, but the material does not supply a sufficient amount of oxygen to the eyeballs. Also, the growth of bacteria is accelerated on a soft contact lens when it is exposed to water. Thus, the development of a material having higher oxygen permeability as well as a resistance to the lens contamination from bacteria has been demanded in the art.    Prior Art Document 3: U.S. Pat. No. 5,760,100    Prior Art Document 4: Japanese Laid-open Patent Publication No. 2007-70405
A contact lens using only a silicone polymer has also been proposed in view of oxygen permeability (See, Prior Art Document 5). A silicone contact lens manufactured from a silicone polymer composition as a base material is satisfactory in flexibility, oxygen permeability and transparency. However, because such a contact lens has poor affinity to the surface of the eyeballs as being hydrophobic and water-repellent which are the properties of the silicone itself, it may irritate the corneal tissue to cause inflammation.    Prior Art Document 5: Japanese Laid-open Patent Publication No. 51-131562
Thus, the surface of a silicone contact lens has been modified by graft polymerizing a hydrophilic compound into the surface of the contact lens film using an ionizing radiation (See, Prior Art Document 6) or by subjecting it to the electrically discharging treatment under vapor-containing atmosphere (See, Prior Art Document 7). However, these methods only modifies the surface of the contact lens temporarily to a level that the affinity of the silicone may be improved and are not directed to the above-described attachment of the bacteria.    Prior Art Document 6: Japanese Laid-open Patent Publication No. 51-27546    Prior Art Document 7: Japanese Laid-open Patent Publication No. 54-81363